1. Field of the Invention
This invention relates to a sensor system for monitoring fluid level and displacement and, more particularly, to a sensor system for monitoring the level of crude oil in storage containers.
2. Background Art
There are many types of sensors known in the art for monitoring fluid level, and especially for measuring the level of crude oil in storage containers. Many of these sensors utilize a float designed to interact with the sensor. These sensors can be expensive in order to obtain the accuracy necessary and are often affected by the fluids and other contaminates associated with storage containers in which such fluids are stored. The following is a listing of known sensors for monitoring or measuring fluid level and disadvantages of such sensors.
Linearly Variable Differential Transformers (VDT) require high precision manufacturing of the coils and a sensor length of more than two times the useful length of the sensor. They also have resolution that is limited by the resolution of their data acquisition system and by the electrical noise of the whole system.
Ultrasonic transducers are affected by changes in pressure, temperature and other variations in the composition of the media in which they operate due to their sensitivity to the density of the media. This limitation thereby increases the probability of errors.
Reed switch arrays, used in the oil industry, provide an incremental readout with limited resolution. However, they are sensitive to shock and vibrations and can be damaged by electrical storms. Furthermore, they are labor intensive to manufacture, which makes them expensive, and are unreliable due to the hundreds of switch contacts and internal connections. The accuracy of such arrays is typically +/- 6.4 mm and clearance required between a float used with such reed switch arrays and the sensor elements must be between 0-3 mm. The arrays also require yearly cleaning and float replacement due to contaminant buildup.
Optical encoders are sensitive to contamination and are expensive. They also require high precision during manufacturing and implementation.
Magnetostrictive wave guide transducers are expensive and require high precision electronics. Also, the clearance between the float and the sensing element is limited.
Radar is expensive and has limited accuracy.
Capacitive probes are expensive and very sensitive to contamination. They also require high precision electronics and have a limited range.
Pressure transducers can be affected by contamination and have a resolution limited by the acquisition system employed.
It is an object of the present invention to provide a fluid sensor system that is inexpensive and easy to manufacture, has high reliability and accuracy, is easy to implement, and has a low sensitivity to contamination, shock, electrical storms and the media in which it operates.
It is an object of the present invention to provide a fluid sensor system having a float that includes an activatable resonator circuit.
It is an object of the present invention to provide a fluid sensor system having two or more floats each responsive to a different frequency excitation signal.
It is an object of the present invention to provide a fluid sensor system having two or more floats each responsive to a common excitation frequency and each having a resonating circuit that is activatable independent of resonating circuits of other floats.